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The Keys to Cat-ness

What makes Maine coons cuddly and Russian shorthairs standoffish? The answer may lie in the first sequence of the cat genome, published today. In all, geneticists have turned up 20,285 genes, the analysis of which could shed light on everything from human diseases to the underpinnings of feline domestication.

Cats now join a growing list of mammals whose DNA has been deciphered. Close-up views of the DNA of chimps, macaques, mice, rats, and dogs have given scientists important clues to how our own genome works, including where genes are and how they are regulated (ScienceNOW, 7 December 2005). The cat genome should help us understand our DNA even better.

The latest sequence comes courtesy of a 4-year-old Abyssinian cat named Cinnamon. The analysis is only a first pass and so is not as complete as that done for humans or dogs. Still, evolutionary biologist Stephen O'Brien and bioinformaticist Joan Pontius of the National Cancer Institute in Frederick, Maryland, and their colleagues were able to decipher about 65% of the gene-containing parts of the genome, or more than 20,000 genes. That's perhaps 95% of the total, based on comparisons with other genomes.

Based on the structure of the chromosomes, the cat genome much more closely resembles that of humans than that of other nonprimate species. Unlike cats and humans, pieces of chromosomes in "the dog, mouse, rat, and others have been reshuffled like a poker deck," says O'Brien. This conservation suggests that the cat's genome has more in common with the ancient ancestor of cats, humans, and other mammals than, say, the dog's does. Other surprises included an excessive amount of mitochondrial DNA stuck into the cat genome, although researchers have yet to figure out the reason or significance.

The cat genome is revealing secrets of disease as well. Collaborator Kristina Narfström of the University of Missouri, Columbia, found the genetic cause of an eye disease called retinitis pigmentosa that runs in Cinnamon's breed. Understanding how this and other disease genes function in cats will shed light on human health, says geneticist Leslie Lyons of the University of California, Davis.

Lyons also notes that the fact that the cat genome hasn't changed very much through time makes it useful for understanding evolution. "The cat helps to define important aspects of being a carnivore and potentially genes involved with domestication or for being a cat," she says. "Comparisons to the dog, for example, will help define 'catness.' " It may be possible to determine the genetic basis for a carnivore's meat-eating metabolism, Lyons notes, and to track down behavioral genes that make cats more curious than dogs.

Lyons and others argue that the cat genome needs to be sequenced more thoroughly for it to be truly valuable to health and other studies. And that's in the works, says O'Brien, with fuller coverage expected in the next year or so. Two dozen other genomes, including those of a fruit bat and a mole, are also in the pipeline for light sequencing and analysis.